Method of obtaining fingerprints



Patented Jan. 21, 1936 UNITED STATES PATENT OFFICE No Drawing. Application March 14, 1935,

Serial No. 11,105

10 Claims.

This invention relates to a method of obtainin finger prints.

At the present time when conditions such as poor light, inaccessibility, et cetera, make it dinicult or impossible to obtain a photograph of. finger prints, it is the custom to sprinkle powder on said finger prints, and after brushing off the surplus powder, taking an impression by means of a piece of tape. The impression so obtained is not as clear and distinct as it should be, and it is my object to produce an entirely new powder, and by using it in combination with a sensitized sheet treated with my solution, to obtain finger print impressions which are distinct and clear.

My new finger print powder preferably consists of hydroquinone and acacia ground together. Best results are obtained if the powder is ground fine enough to pass through silk. The hydroquinone should preferably exceed the acacia by weight; and I have secured good results by using eight parts hydroquinone and one part acacia by weight, although this proportion can be varied considerably and still obtain satisfactory results. The hydroquinone is a reducing agent, and other reducing agents such as metol could be used, al-

though I prefer hydroquinone. Likewise the acacia is a water soluble gum, and while I prefer acacia, other water soluble gums might be used.

Acacia is sometimes called gum arabic.

In practicing my method I use a sensitized sheet such as photographic film or sensitized paper in taking the finger print impression, first wetting it in an alkaline solution preferably consisting of sodium hydroxide, sodium sulphite and water.

To make this solution I use 25 grams sodium hydroxide, 25 grams sodium sulphite and add sufficient water to make one liter, although these proportions may be varied. The sensitized sheet is soaked in this solution for one or two minutes before taking the impression as will be explained later.

After the impression has been taken the sensitized sheet is put in an acid fixing bath commonly used by photographers. One formula consists of the following:

Water 500 cc. Hypo (sodium thiosulphate) 240 grams. Sodium sulphite 15 grams. 5O Acetic acid (28%) 47.5 cc.

Boric acid, crystals 7.5 grams. Potassium alum 15 grams. Add water to make one liter.

Other well known formulas may be used to 55 make the acid fixing bath.

In practicing my method I first sprinkle on the finger prints the powder consisting of a reducing agent such as hydroquinone and a water soluble gum such as acacia, ground together as previously described. The finger print lines are then 5 brushed out carefully in accordance with the present practice. A sensitized sheet is soaked in an alkaline solution for one or two minutes, which solution may consist of sodium hydroxide, sodium sulphite and water, as previously described. The 10 excess moisture is then removed from the sensitized sheet by some suitable means such as filter paper or lintless blotter, and said sensitized sheet is placed face down on the finger print and pressed down to eliminate any air bubbles. The sensi- 15 tized sheet is then lifted oif and when the development of the impression on it is distinct enough it is promptly placed, for about three minutes, in an acid fixing bath such as previously described, to fix the picture on said sensitized 0 sheet, and then it is rinsed in clear water and allowed to dry. This bath arrests further development, prevents darkening of. the picture, and cleans 01f any stains.

The hydroquinone reacts chemically with the 25 silver bromide in the sensitized sheet, reducing said silver bromide to free silver. This reaction results only when said sheet has had the alkaline solution applied to it. This gives a black print on the sensitized sheet. The black begins to 30 appear as soon as the powder comes in contact with the sheet, and the impression usually becomes distinct in a minute or less.

The sodium hydroxide in the alkaline solution speeds up the appearance of the black print on 35 the sensitized sheet, while the sulphite in said solution is for the purpose of preventing the formation of brown stains.

The hydroquinone in the finger print powder is a reducing agent only in an alkaline solution, 40 consequently it is necessary to wet the sensitized sheet in an alkaline solution to get the results desired. The acacia acts as a binder between the finger print and the powder of which it forms a part. 45

What I claim is:

1. The method of obtaining a finger print im pression comprising placing a powder embodying a substance which is a reducing agent in an alkaline solution, on the finger print, placing a, sensitized sheet which has been wet with an alkaline solution on said powderedfinger print, and removing said sensitized sheet and wetting it with an acid fixing bath.

2. The method of obtaining a finger print impression comprising placing a powder embodying a substance which is. a reducing agent only in an alkaline solution, on the finger print, placing a sensitized sheet which has been wet with an alkaline solution on said powdered finger print, removing said sensitized sheet and wetting it with an acid fixing bath, and then washing said sensitized sheet with clear water.

3. The method of obtaining a finger print impression comprising placing a powder embodying a substance which is a reducing agent in an alkaline solution and a binding agent, on the finger print, placing a sensitized sheet which has been wet with an alkaline solution on said powdered finger print, and removing said sensitized sheet and wetting it with an acid fixing bath.

4. The method of obtaining a finger print impression comprising placing apowder embodying hydroquinone and a water soluble gum on the finger print, placing a sensitized sheet which has been wet with an alkaline solution on said powdered finger print, and removing said sensitized sheet and wetting it with an acid fixing bath.

5. The method of obtaining a finger print impression comprising placing a powder embodying hydroquinone and a water soluble gum on the finger print, the said hydroquinone exceeding the said water soluble gum by weight, placing a sensitized sheet which has been wet with an alkaline solution on said powdered finger print, and removing said sensitized sheet and wetting it with an acid fixing bath.

6. The method of obtaining a finger print impression comprising placing a powder embodying hydroquinone and acacia, on the finger print, the said hydroquinone exceeding the said acacia by weight, placing a sensitized sheet which has been wet with an alkaline solution on said powdered finger print, and removing said sensitized sheet and wetting it with an acid fixing bath,

7. The method of obtaining a finger print impression comprising placing a powder embodying hydroquinone and acacia, on the finger print, placing a sensitized sheet which has been wet with an alkaline solution embodying sodium sulphite on said powdered finger print, and removing said sensitized sheet and wetting it with an arid fixing bath.

8. The method of obtaining a finger print impression comprising placing a powder embodying hydroquinone and acacia, on the finger print, the said hydroquinone exceeding the said acacia in the said powder by weight, placing a sensitized sheet which has been wet with a solution embodying sodium hydroxide, sodium sulphite and water, on said powdered finger print, and removing said sensitized sheet and wetting it with an acid fixing bath.

9. The method of obtaining a finger print impression comprising placing a powder embodying hydroquinone and acacia, on the finger print, the said hydroquinone exceeding the said acacia in the said powder by weight, placing a sensitized sheet which has been wet with a solution embodying sodium hydroxide and sodium sulphite in substantially equal parts and water, on said powdered finger print, and removing said sensitized sheet and wetting it with an acid fixing bath.

10. The method of obtaining a finger print impression comprising placing a powder embodying hydroquinone and acacia, on the finger print, the said hydroquinone exceeding the said acacia in the said powder by weight a plurality of times, placing a sensitized sheet which has been wet with a solution embodying sodium hydroxide and sodium sulphite in substantially equal parts and water, on said powdered finger print, and removing said sensitized sheet and wetting it with an acid fixing bath.

JUSTIN J. MCCARTHY.

CERTIFICATE OF CORRECTION.

Patent No. 2,028,619.

January 21, 1936.

JUSTIN J. MCCARTHY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 8', claim '7, for "arid" read acid; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5rd day of March, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

